An ultrasonic piezoelectric transducer device typically includes a piezoelectric membrane capable of vibrating in response to a time-varying driving voltage to generate a high frequency pressure wave in a propagation medium (e.g., air, water, or body tissue) in contact with an exposed outer surface of the transducer element. This high frequency pressure wave can propagate into other media. The same piezoelectric membrane can also receive reflected pressure waves from the propagation media, and convert the received pressure waves into electrical signals. The electrical signals can be processed in conjunction with the driving voltage signals to obtain information on variations of density or elastic modulus in the propagation media.
While many ultrasonic transducer devices that use piezoelectric membranes are formed by mechanically dicing a bulk piezoelectric material or by injection molding a carrier material infused with piezoelectric ceramic crystals, devises can be advantageously fabricated inexpensively to exceedingly high dimensional tolerances using various micromachining techniques (e.g., material deposition, lithographic patterning, feature formation by etching, etc.). As such, large arrays of transducer elements are employed with individual ones of the arrays driven via beam forming algorithms. Such arrayed devices are known as pMUT arrays.
Generally, for any ultrasonic transducer technology, there is a tradeoff between imaging resolution, which improves with higher frequencies, and penetration depth, which improves lower frequencies. To date, pMUT arrays have limited bandwidth (e.g., fractional bandwidth being well under 1). As such, transducers employing pMUT arrays are typically application specific, with for example Gasrointestinal Ultrasonography requiring a transducer of a first operational frequency band, perhaps 2-6 MHz, and Echocardigraphy requiring a transducer of a second operational frequency band, perhaps 5-13 MHz. A pMUT array capable of multi-frequency operation and/or dynamic frequency tuning would advantageously permit an ultrasonic transducer operator to modulate the operational (transmit and/or receive) frequency band of the transducer while imaging a specimen or patient and eliminate any need to change transducers.